1. Field of the Invention
The present invention relates generally to imaging systems and more particularly to imaging systems for use in nuclear medicine.
2. Description of the Relevant Art
Gamma ray cameras are used in nuclear medicine to generate high quality images for brain, SPECT (Single Photon Emission Computer Tomograph), and total body bone studies. These cameras are most frequently used for cardiac and total body bone studies.
It is very important that the gamma ray camera be designed for high patient throughput for both economic and therapeutic reasons. The cost for diagnosing each patient is reduced if more patients can be diagnosed per unit time. For very sick patients or patients in intensive care it is important to minimize the time required to acquire image data. Patient throughput is increased if imaging time is reduced. Other factors, such as patient set-up time also affect patient throughput.
Modern gamma ray cameras utilize detectors, such as Anger cameras, having a wide field of view so that it is possible to image the full width of the body of a patient at each angular stop without the requirement of rectilinear scanning. These detectors use thick lead collimators to focus images and are thus very heavy. The collimators must be positioned as close to the patient as possible to acquire image data required to generate high resolution images. The image data acquired by the detectors is processed by a computer to generate an image. Techniques for processing image data are well-know in the art and described in xe2x80x9cPrinciples of Instrumentation in SPECTxe2x80x9d by Robert Eisner, Journal of Nuclear Medicine, Vol. 13, #1, March 1985, pp. 23-31; Computed Tomography in Nuclear Medicinexe2x80x9d by John Keyes, (chapter in) Computer Methods, C. V. Mosley, St. Louis, 1977, pp. 130-138; and xe2x80x9cSingle Photon Emission Computed Tomography,xe2x80x9d by Bernard Oppenheim and Robert Appledown, (chapter in) Effective Use of Computers in Nuclear Medicine, Michael Gelfand and Stephen Thomas, McGraw-Hill Book Co., New York 1988, pp. 31-74.
Recent technological innovations have produced dual-head systems, with two detectors having their detector image direction arrows oriented at a fixed angle of 180xc2x0, and triple-head systems, with three detectors having their image direction arrows oriented at fixed angles of 120xc2x0, SPECT gamma ray cameras capable of rapid, high quality SPECT imaging. FIGS. 1A and 1B are schematic diagrams depicting the fixed orientation of the detector image direction arrows 2 of the detectors 4 in a dual-head and triple-head system.
When the detectors rotate about the patient, a lateral axis is defined as the mechanical axis of rotation aligned with the computer matrix for reconstructing the SPECT images.
The single, dual, and triple head cameras each have certain features which are advantageous for a particular type of application. To determine which system is best for a particular application factors such as 1) the ability of the camera to perform required imaging tasks; 2) the quality of the images generated, and 3) patient throughput should be considered.
The acquisition of data for a total body scan requires movement of the detector along the length of the patient""s body. The dual-head system is very efficient because image data for anterior/posterior images can be acquired simultaneously. The time required to complete a scan can be reduced from 45 to 60 minutes, for a single-head camera, to 30 minutes. The triple-head system is no more efficient than the single-head system because the detectors cannot be aligned to acquire simultaneous anterior/posterior or left/right lateral data.
To generate high-quality SPECT for brain, bone, or liver studies views taken along a complete 360xc2x0 circle (360xc2x0 scan) around the body of the patient are required. Typically, about 64 to 128 angular stops are required to acquire the image data. The above-described dual-head camera reduces the imaging time to xc2xd the imaging time of a single-head system because data is acquired from two stops immediately. The triple-head camera reduces the imaging time to about ⅓ the imaging time of a single-head system because data is acquired from three stops simultaneously.
For cardiac SPECT studies, the analysis of complex imaging considerations has lead to use of at least 32 stops over a 180xc2x0 arc about the patient""s body (180xc2x0 scan). For a 180xc2x0 scan the imaging time of a single-head and dual-head system are the same because only one detector of the dual-head system is within the 180xc2x0 arc at any given time. A triple-head system reduces the image time to about ⅔ the time of a single-head system for a 180xc2x0 scan because two detectors are within the 180xc2x0 arc about ⅓ of the time.
In view of the above it is apparent that the mechanical system for orienting the detectors must be designed to provide a mechanism for accurately orienting the detectors at various angular stops relative to the patient and to position the collimator as close to the patient as possible. Additionally, the system must be stable so that the heavy detectors are held still at each stop to facilitate the acquisition of accurate imaging data. Other attributes that are required of the mechanical system are ease of patient positioning, size of footprint, and overall size.
Further, as described above, the existing systems each have advantages for particular applications but generally lack the flexibility for optimal performance over a range of applications. Additionally, although cardiac SPECT imaging accounts for about 33% of the use of gamma ray cameras, none of the systems significantly reduce the imaging time for the 180xc2x0 scan used in forming cardiac SPECT images.
The present invention is a unique system for reducing the imaging time required to generate a 180xc2x0 SPECT image.
According to one aspect of the invention, the angular displacement between two detectors may adjusted to any angle between about 90xc2x0 and 180xc2x0 and the detectors can be rotated to any desired angular position along a circular path centered on a lateral axis. Thus, the system can be optimally configured for total body scans and 360xc2x0 SPECT (relative angular displacement of 180xc2x0) and 180xc2x0 SPECT (relative angular displacement of 90xc2x0) to provide a very flexible system.
According to a further aspect of the invention, each detector can be independently rotated along different circular paths centered on the lateral axis.
According to another aspect of the invention, both detectors are coupled to a single pair of rings. Each of the rings has an arc shaped groove which is substantially parallel to the circumference of the ring and aligned with the arc-shaped groove in the other ring. The second detector is coupled to the groove via guide rollers mounted to a support arm attached to the second detector which allows the second detector to move along the groove so as to vary the lateral displacement, relative to the lateral axis, between the first and second detectors to a selected magnitude having a value of between 90xc2x0 and 180xc2x0.
According to another aspect of the invention, each detector is separately coupled to a first and second pair of rings respectively. Each of the first pair of rings has a radial support flange that is integral with and perpendicular to the inner surface of each of the first pair of rings. The second pair of rings is positioned on the radial support flange of each of the first pair of rings to that the second pair of rings is displaced laterally away from the first pair of rings and is disposed between the first pair of rings. The second pair of rings may be rotated independent of the first pair of rings to adjust the angular displacement between the detectors to a predetermined magnitude.
According to another aspect of the invention, each detector may be independently moved toward or away from the lateral axis.